Maximum yield of foreign lipase in Escherichia coli HB101 limited by duration of protein expression

The Influence of Nutrient Medium Composition on Escherichia coli Biofilm Development and Heterologous Protein Expression

In the present study, the effects of different nutrient media on the development of Escherichia coli biofilms and the production of a heterologous protein were examined. E. coli JM109(DE3) cells transformed with pFM23 plasmid carrying the gene for enhanced green fluorescent protein (eGFP) expression were used. Cells were grown in two different culture media, Lysogenic Broth (LB) and M9ZB, in a flow cell system for 10 days. Epifluorescence microscopy, fluorimetry, and a high-performance liquid chromatography (HPLC) method based on hydrophobic interaction chromatography (HIC) were used to assess bacterial growth, plasmid copy number (PCN), and eGFP production in both planktonic and biofilm cells. The results showed that biofilm development was favored in M9ZB medium when compared with LB. However, the number of eGFP-expressing cells was higher in LB for both planktonic and sessile states (two-fold and seven-fold, respectively). In addition, the PCN in biofilm cells was slightly higher when using LB medium (on average, 29 plasmids per cell versus 20 plasmids per cell in M9ZB), and higher plasmid stability was observed in biofilms formed in LB compared to their planktonic counterparts. Hence, E. coli biofilms grown in LB enhanced both plasmid stability and capacity to produce the model heterologous protein when compared to M9ZB.

Impact of signal peptide and transmembrane segments on expression and biochemical properties of a lipase from Bacillus sphaericus 205y

A total of 97 amino acids, considered as the signal peptide and transmembrane segments were removed from 205y lipase gene using polymerase chain reaction technique that abolished the low activity of this enzyme. The mature enzyme was expressed in Escherichia coli using pBAD expression vector, which gave up to a 13-fold increase in lipase activity. The mature 205y lipase (without signal peptide and transmembrane; -SP/TM) was purified to homogeneity using the isoelectric focusing technique with 53% recovery. Removing of the signal peptide and transmembrane segments had resulted in the shift of optimal pH, an increase in optimal temperature and tolerance towards more water-miscible organic solvents as compared to the characteristics of open reading frame (ORF) of 205y lipase. Also, in the presence of 1mM inhibitors, less decrease in the activity of mature 205y lipase was observed compared to the ORF of the enzyme. Protein structure modeling showed that 205y lipase consisted of an α/β hydrolase fold without lid domain. However, the transmembrane segment could effect on the enzyme activity by covering the active site or aggregation the protein.

Optimization of recombinant protein expression level in Escherichia coli by flow cytometry and cell sorting

Overexpression of recombinant proteins in Escherichia coli often leads to a severe growth retardation of the host cells. The phage T7 promoter phi10 in a pET vector was utilized to express human superoxide dismutase. Induction with IPTG lead to an increase in protein content and cell size and a termination of cell division, due to the deviation of the general metabolic fluxes from all cellular processes to plasmid maintenance and foreign protein synthesis. To generate promoter mutants which are better tolerated by the host cells we constructed a random mutation library by PCR with degenerated primers in a part of the promoter involved in the binding to the RNA polymerase and the initiation of transcription. This library was sorted by flow cytometry for cells with a lower total protein content as an indicator for continued cell replication and hence a less severe stress situation. The clones obtained had a similar SOD production compared to the original strain, but were able to reach higher densities in a batch culture, which resulted in a higher total yield.

Flow cytometric analysis of metabolic stress effects due to recombinant plasmids and proteins in Escherichia coli production strains

Overexpression of recombinant proteins in Escherichia coli often leads to a severe growth retardation of the host cells. Using flow cytometry, we analyzed the temporal development of the cellular content of DNA, total protein, and the recombinant product (human superoxide dismutase) in different strains. In cells carrying plasmids utilizing the phage T7 promoter 10 (pET vectors), induction with IPTG leads to an increase in protein content and size, an increase and a wide spreading of DNA content distribution, and a termination of cell division. These effects occurred with pET plasmids with or without an insert, but not with another plasmid which utilizes the tac promoter.